netdev - Re: Question about tg3 and bnx2 driver suppliers

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Message-ID: <20110220124115.730eca80@nehalam>
Date:	Sun, 20 Feb 2011 12:41:15 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Micha Nelissen <micha@...i.hopto.org>,
	Michael Durket <durket@...hwire.stanford.edu>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: Question about tg3 and bnx2 driver suppliers

On Sun, 20 Feb 2011 20:17:00 +0100
Eric Dumazet <eric.dumazet@...il.com> wrote:

> Le dimanche 20 février 2011 à 19:19 +0100, Micha Nelissen a écrit :
> > Eric Dumazet wrote:
> > > One possible cause of packet drops is when softirqs are disabled for too
> > > long periods, even if NIC has a big RX ring (check ethtool -g eth0)
> > 
> > Why aren't the softirqs converted to workqueues? Wouldn't that cut 
> > dependencies to other softirq users and improve latency?
> > 
> 
> Because it was done like that in the old days.
> 
> Its a bit less important these days, now typical machines have 8+ cpus.
> Each device interrupt can be handled by its own cpu :)

The latency to schedule a work queue is still much higher
than the latency to do a softirq. Last time I played around with it,
things like loopback performance dropped 10% if using work queue.
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